Kamailio

Kamailio is an open-source SIP server, formerly known as OpenSER, with a history tied to SIP Express Router (SER). Licensed under GPL-2.0-or-later, it functions as a registrar, proxy, or redirect server, offering features like presence support, RADIUS/syslog accounting, remote control via XML-RPC and JSON-RPC, and support for SQL and NoSQL backends. The name Kamailio is Hawaiian, meaning "to converse."

Written in pure C with architecture-specific optimizations, Kamailio serves various scenarios from small offices to carrier services as a SIP signaling server. Its features include a telephony system, load balancer, security firewall, least cost routing engine, IMS/VoLTE platform, instant messaging and presence services, IPv4-IPv6 gateway, MSRP relay, and SIP-WebRTC gateway.

Kamailio is utilized by major ISPs like 1&1 and sipgate for large-scale deployments. OpenSIPS, a fork of SER, diverged from Kamailio's codebase and is known for handling voice, text, and video communications, compliant with RFC 3261 and recognized by Google in 2017.

Kamailio's roots trace back to 2001 when SER was developed at Fraunhofer FOKUS. The code was GPL'd in 2002, with the first fork, OpenSER, emerging in 2005. By 2012, OpenSER and SER converged under Kamailio. A timeline highlights key events: third-party contributions in 2002, the move of FOKUS team members in 2004, OpenSER's rename to Kamailio in 2008, collaboration plans with SER developers in 2008, and the first Kamailio World conference in Berlin by FOKUS and the community in 2013.